feat(KB-504): add migration and first-run experience for multi-project support

- Add MigrationOrchestrator with filesystem scanning and auto-registration

- Add FirstRunExperience with setup wizard state management

- CLI integration with automatic migration hook on first run

- Backward-compatible single-project mode support

- \"--project\" flag support for CLI multi-project targeting

- KB_SKIP_MIGRATION environment variable for recovery

- Graceful fallback when central database unavailable

- New fn init command to initialize kb projects

- Interactive first-run setup wizard API in dashboard

packages/dashboard/src/__tests__/project-routes.test.ts

@@ -76,7 +76,7 @@ import {
   fetchTasks,
   type ProjectInfo,
   type DetectedProject,
-} from "../../app/api";
+} from "../../app/api.js";
 
 function mockFetchResponse(
   ok: boolean,